Hydraulic drives are used among other things to open and close valves, e.g. for gas turbines. Since in this context, high forces must be applied in order to close a valve, particularly in an emergency, at short notice and potentially over large operating ranges, hydraulic drives are preferentially used.
A linear movement can be produced by the combination of e.g. a rotatory pump and a lifting cylinder. The axial position of the piston within the lifting cylinder is thereby directly controlled by the setting of a hydrostatic pressure within the hydraulic system via the pump.
In this regard, printed publication EP 2 620 655 A1 discloses a piston cylinder having a return spring so that the return spring can extend the piston and a coupled valve closes. The coupled valve is opened by a source of volumetric fluid flow, which is driven by a servomotor, supplying a fluid to the piston cylinder and increasing the hydrostatic pressure such that the piston retracts. According to EP 2 620 655 A1, the fluid flow source can pump the working fluid in two different directions so that the piston can be both retracted as well as extended by means of the driven pump. Upon a malfunction, a parallel logic controls a valve, for example, in order to couple the inflow and the outflow of the piston cylinder such that the piston is extended via the return spring and the coupled valve closes.